Outlet silencer and heat recovery structures for gas turbine

ABSTRACT

A sound attenuating duct unit suitable for connection to an outlet of a gas turbine and an improved heat recovery apparatus for use with such a turbine are disclosed. The former unit includes a duct housing having exterior sides, an air inlet at one end and first and second air outlets. Interior walls define a main airflow passageway extending from the air inlet to both of the outlets. Sound absorbing and heat insulation material is arranged between these walls and the exterior sides. Sound attenuating members are mounted in the passageway and a diverter damper is mounted in the housing and is able to direct air flow to either one of the air outlets. The sound attenuating members are mounted between the diverter damper and the air inlet. The heat recovery apparatus includes a series of aerodynamic diffusers mounted in a housing adjacent an air flow inlet connectable to the gas turbine.

BACKGROUND OF THE INVENTION

[0001] This invention relates to duct units and other devices that canbe connected to an air flow outlet of a machine having a rotating axialflow member, for example, a gas turbine and the invention furtherincludes heat recovery apparatus.

[0002] The use of large gas turbines for generating electrical power iswell known in the power generation art. These large gas turbines can bemounted horizontally in a building or other shelter that providesprotection to the turbine against the elements. The outlet for theturbine, through which passes a hot air flow at substantial speed, canbe connected to a diffuser duct of cylindrical configuration and then toa transition duct which transforms the hot air outlet passageway from acircular cross-section to a rectangular cross-section. A damper can thenbe provided, which damper in a first position can direct the hot airflow upwardly through a suitable outlet stack (also referred to as aby-pass stack) which can, in some cases, include some form of silencerarranged in a duct section in order to reduce the level of sound exitingfrom the stack. If the damper is moved to another position, the hot aircan be directed through another pipe section to a heat recovery system,ie. a heat recovery steam generator. The known heat recovery steamgenerators can be quite tall and they can include an exterior housing inwhich is mounted an array of heat exchanging units. Each heat exchangingunit can comprise a series of heat exchanging pipes through which aliquid such as water flows. The flowing water is heated by the hotexhaust gases from the turbine resulting in the generation of steam.

[0003] The known hot gas outlet arrangements designed for attachment tothe outlet of a gas turbine of the aforementioned type suffer fromseveral disadvantages and deficiencies. For example, the known outletstack arrangements, even if they are provided with some form of ductsilencer, are not very efficient at reducing the level of sound exitingfrom the gas turbine. One reason for this is that the silencer module,if it is provided at all, may be spaced a substantial distance from theoutlet of the gas turbine and, due to its location, the silencer duct isnot particularly efficient in terms of sound reduction due to thetransmission of sound through the walls of the ducts located upstream ofthe silencer. Also, if the diverter damper is directing the hot air flowinto a heat recovery apparatus rather than straight through the by-passstack, a silencer duct located along the path for the by-pass stack willbe useless in reducing the amount of noise generated by the turbine andexiting from the hot air outlet system.

[0004] A further substantial difficulty with the known heat recoveryapparatus used downstream from a gas turbine is that the hot air fromthe turbine is not directed evenly over the heat exchanging units whichmay be mounted in series in a tower-like housing. If the hot air isdistributed unevenly, then this will result in uneven heating of theheat exchanging fluid flowing through the heat exchanging units,reducing the efficiency of the heat recovery for the steam generator.Also, uneven hot air distribution in the heat recovery apparatus canresult in excessive pressure loss in this apparatus, reducing the gasturbine efficiency.

[0005] It is one object of the present invention to provide an improvedsound attenuating duct unit suitable for connection to an air flowoutlet of a rotating axial flow machine, such as a gas turbine, and ableto provide a greater level of sound reduction than is achieved withexisting known sound attenuating devices used in combination with such amachine.

[0006] It is a further object of the present invention to provide a newsound attenuating duct unit which employs sound attenuating memberslocated between a diverter damper mounted in the duct housing and an airinlet of the duct unit.

[0007] It is another object of one aspect of this invention to simplifythe silencer modules used in known by-pass stacks and main exhauststacks, thereby achieving less pressure drop and reducing manufacturingcosts.

[0008] It is a further object of the present invention to provide a heatrecovery apparatus which includes a housing containing an array of heatexchanging units and a series of aerodynamic diffusers adjacent an inletof the housing, the diffusers acting to redirect a substantial portionof incoming hot air in order that this hot air will pass more uniformlythrough the heat exchanging units.

[0009] It is another object of one aspect of the present invention toprovide a new diverter section for a machine having a rotating axialflow member, this section capable of reducing greatly the pressure dropwhen air passes through it.

SUMMARY OF THE INVENTION

[0010] According to one aspect of the invention, a sound attenuatingduct unit suitable for connection to an airflow outlet of a machinehaving a rotating axial flow member includes a duct housing havingexterior sides and two opposite ends. An air inlet is located in one ofthese ends and the housing further includes first and second air outletswith the first air outlet located at the other end of the housing. Theair inlet is adapted for connection to the airflow outlet of themachine. Interior walls are arranged in the housing and define a mainairflow passageway system which extends from the air inlet to both ofthe first and second outlets. Sound absorbing material is arrangedbetween the interior walls and the exterior sides of the duct housingand sound attenuating members are mounted in the airflow passagewaysystem. A diverter damper is mounted in the duct housing and is movablebetween a first position where the damper directs airflow enteringthrough the air inlet to the first air outlet and a second positionwhere the damper directs the air flow to the second air outlet. Thesound attenuating members are mounted between the diverter damper andthe air inlet so as to reduce the sound levels emitted through either ofthe air outlets during use of the duct unit.

[0011] Preferably the sound attenuating members comprise a series ofsplitters rigidly mounted in the airflow passageway system and dividingthe main air flow passageway system into smaller passageways.

[0012] According to another aspect of the invention, a sound attenuatingduct unit suitable for connection to an outlet of a stationary gasturbine includes a duct housing having exterior sides, an air inlet inone end of the housing that lies in a first plane, and first and secondair outlets with the first air outlet located in one of the exteriorsides of the housing spaced from said one end and the second air outletlocated in another of the exterior sides that extends in a second planearranged at a substantial angle to the first plane. The air inlet isadapted for connection to the outlet of a gas turbine in order toreceive hot air flow from the turbine. Interior walls are arranged inthe housing and define side walls of a main airflow passageway thatextends from the air inlet to both of the first and second outlets.Sound absorbing material is arranged between the interior walls and theexterior sides of the housing. A series of sound absorbing splitters arerigidly mounted in the air flow passageway and extend transversely fromone side of the main airflow passageway to an opposite side thereof. Thesplitters divide the main air flow passageway into smaller passagewaysand contain sound attenuating material capable of withstanding high airflow temperatures of gas turbine exhaust air. A diverter damper ismounted in the duct housing and is movable between a first positionwhere the damper directs the hot air flow to the first air outlet and asecond position where the damper directs this hot air flow to the secondair outlet. The series of splitters are mounted between the diverterdamper and the air inlet so that the hot air flow exiting from thesmaller air passageways flows to a selected one of the first and secondair outlets.

[0013] Preferably this duct unit includes a central air flow definingmember rigidly mounted in the housing and extending inwardly from theair inlet to the series of splitters.

[0014] According to a further aspect of the invention, a heat recoveryapparatus includes a housing having exterior walls, a hot airflow inletand an airflow outlet. An array of hot exchanging units is mounted inthis housing, each heat exchanging unit being adapted for heat exchangebetween a hot air flow and a heat exchanging liquid flowing throughpipes of the heat exchanging unit. A series of aerodynamic diffusers aremounted in the housing adjacent the air flow inlet. The aerodynamicdiffusers redirect at least a substantial portion of hot air flowentering the housing through the air flow inlet during use of theapparatus in order that the hot air flow passes more uniformly throughthe heat exchanging units.

[0015] Preferably the aerodynamic diffusers extend horizontally and arearranged one above another.

[0016] Further features and advantages will become apparent from thefollowing detailed description of the various aspects of the invention,taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic elevation of a known system for generatingpower by means of a large gas turbine mounted horizontally in aprotective structure, the illustrated system including a pair of outletstacks and a heat recovery steam generator;

[0018]FIG. 2 is a side elevation of a sound attenuating duct unitconstructed in accordance with the invention, this view alsoillustrating a section of a by-pass stack;

[0019]FIG. 3 is a horizontal cross-section taken along the line III-IIIof FIG. 2, this view showing splitters arranged in the duct section;

[0020]FIG. 4 is a velocity profile illustrating the advantage of turningvanes in a heat recovery apparatus such as a heat recovery steamgenerator, this view illustrating the uniform low velocity air passingthrough the region where heat exchanging units would be located;

[0021]FIG. 5 is a vertical cross-section of an aerodynamic diffuser orturning vane that can be used in the heat recovery apparatus of theinvention;

[0022]FIG. 6 is a vertical cross-section of another form of aerodynamicdiffuser that can be used in the heat recovery apparatus;

[0023]FIG. 7 is a schematic illustration of airflow patterns common in aprior art heat recovery apparatus; and

[0024]FIG. 8 is a schematic side elevation of a typical heat recoverysteam generator which can use the aerodynamic diffusers of FIG. 5 orFIG. 6, this view being partly in vertical cross-section in the regionsof the heat exchanging units in order to illustrate same.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0025] Illustrated in FIG. 1 is a schematic view of an electrical powergenerating system employing a large, stationary gas turbine 10. The gasturbine can be of standard construction and it can be protected by meansof a building or structure 12. The turbine can be rigidly mounted on athick concrete pad 14. Intake air for the turbine is drawn in through anair intake filter arrangement 16 which can be mounted on a suitablesupport frame 18. Arranged below the filter arrangement 16 is a gasturbine generator 20 which can be fitted with a suitable generatorcircuit breaker. A circular hot air outlet for the turbine is located at22. Connected downstream of the turbine outlet is a bypass stack 24through which the hot exhaust gases from the turbine can be passed, ifrequired or appropriate. As explained further below, this stack cancontain a duct silencer located in duct section 26 which has an enlargedhorizontal cross-section. Located below the section 26 is a by-passstack module 28 which is open on its right side (as seen in FIG. 1) forinflow of the hot exhaust gases from the turbine. There can be arrangedin this module a diverter damper of known construction which can bemoved from a first position wherein the damper forces the air flow topass upwardly through the bypass stack to a second position where thedamper allows the hot exhaust gases to flow into a heat recovery steamgenerator 30. As explained further hereinafter, the heat recoverysection contains an array of heat exchanging units in which a fluid suchas water flows for purposes of heat exchange with the hot exhaust gasesfrom the gas turbine. Also shown in FIG. 1 is an exhaust gas stack 32 ofknown construction and it is through this stack that exhaust air ofreduced temperature eventually exits to atmosphere after passing throughthe heat recovery steam generator. The bypass stack 24 is shownsupported by a steel supporting framework 34 that extends upwardly fromthe ground.

[0026]FIG. 2 illustrates an improved sound attenuating duct unit 40constructed in accordance with the invention which can be used in placeof the prior art airflow outlet arrangement illustrated in FIG. 1, thatis, in place of the known duct structure that is connected to the outletof the gas turbine, including the bypass stack module 28. The duct unit40 is suitable for connection to an airflow outlet of not only a gasturbine but other machines having a rotating fan or axial flow memberthat generates a significant amount of noise. The duct unit 40 includesa duct housing 42 having exterior sides and two opposite ends includingan end 44 wherein an air inlet indicated at 46 is provided. The exteriorsides of the housing can be constructed of suitable metal plates such asmild steel or stainless steel plates. The illustrated exterior sidesinclude a horizontal top 48, a bottom 50 and two vertically extendingside walls 52 and 54 (see FIG. 3). There is also a sloping wall 56 thatis connected along its lower edge to the top 48 and there is a verticalside wall 58 located opposite the wall 56. Preferably mounted next tothe end 44 of the duct housing is an expansion joint 60 which per se canbe of known construction.

[0027] The duct unit of the invention can include a bypass stack section62, the upper portion of which is not shown in FIG. 2 for ease ofillustration. The upper end of this stack terminates in an air outlet 64where the hot air flow from the gas turbine can exit to atmosphere. Theupper portion of the by-pass stack section 62 is preferably of circularcross-section and, if it is, there can be a transition section 67 whosehorizontal cross-section changes from rectangular (or square) tocircular. As indicated above, the bypass stack can include a widersection (of rectangular, horizontal cross-section) provided for soundattenuation. In the embodiment of FIG. 2, this wider section isindicated at 66 and it can include a plurality of splitter members 68which individually can be of known construction. These splitter memberscan extend from one inner side wall of the section 66 to the oppositeinner side wall and they divide the main airflow passageway into aseries of smaller, parallel passageways 70 which can be as few as four(or less) as shown. In a known manner, these splitters are preferablymade with perforated sheet metal panels 72, 74. These splitter membersare preferably filled with sound attenuating material that is able towithstand the high temperatures of the hot air flow passing through thesection 66. An optional feature of the splitter members 68 is a layer ofstainless steel screen 79, 81 which is arranged behind the perforatedsheet metal, this screen helping to prevent the escape of the soundattenuating material through the holes in the perforated sheet metal.Instead of using this metal screen, it is also possible to encapsulatethe sound attenuating material in woven fiber bags in a manner known perse. If the upper portion of the by-pass stack is circular incross-section, then the splitters 68 are located only in the widersection 66 and they preferably do not extend into the transition section67. This is indicated by the curved ends indicated at 73 in dash lines.

[0028] The illustrated duct unit of FIG. 2 also has another air outletlocated generally at 80. The outlet 80 can be considered as located atthe other or second end of the duct housing, that is the end oppositethe aforementioned end 44. The air outlet 64, sometimes herein referredto as the second air outlet, can be considered as located in a planeindicated at B which, in the illustrated duct unit of FIG. 2, extendshorizontally. The aforementioned air inlet 46 lies in a first planeindicated by the dash line A in FIG. 2 and it will be seen that theplane B lies at a substantial angle to the first plane A. Asillustrated, this substantial angle is 90 degrees.

[0029] The duct unit 40 of the invention also has interior wallsarranged in the duct housing 42 and it is these interior walls whichdefine main airflow passageway system 82, a system which extends fromthe air inlet 46 to both of the first and second outlets. The interiorwalls shown in FIG. 2 include upper and lower transition wall sections84, 86, flat upper wall 88 and lower interior wall 90. The wall 90extends from transition wall 86 to the first air outlet 80 while upperwall 88 extends from the transition wall 84 to an arc-shaped interiorwall section 92 which curves upwardly to the duct section 66. A planarinterior wall section 94 extends upwardly at a small acute angle to avertical plane from a diverter damper 96 to the vertically extendingduct section 66. All of these interior walls are preferably made ofperforated stainless steel sheet metal of suitable composition and ofsufficient thickness (gauge) to withstand high temperature air flows. Itis also possible to construct these interior walls of solid sheet metal(imperforate metal). At least the attenuator section 66 can also beconstructed with perforated interior walls indicated at 100 and 102. Itwill be appreciated that these perforated interior walls can be on allfour sides of the attenuator section 66. If desired, the perforatedinterior walls can extend upwardly along the upper portion of the bypassstack as indicated at 104 and 106 in FIG. 2. It will be understood thatlocated between these interior perforated walls and the exterior wallsis suitable sound absorbing and thermal insulation material 101 whichnot only reduces significantly the volume of sound coming from this ductunit but also serves to insulate the exterior walls of the duct housingfrom the hot gases flowing through the passageway. The use of perforatedsheet metal in the upper portion of the bypass stack will depend uponthe particular job requirements and, in particular, the amount of soundreduction required at the job site. It will be appreciated by thoseskilled in the art that it may not be necessary for the perforatedinterior walls to extend the entire height of the bypass stack in orderto obtain the desired sound attenuation.

[0030]FIG. 3 illustrates additional, vertically extending interior walls108, 110 which can also be perforated and made of stainless steel. Theinterior walls 108, 110 extend through a duct transition section 112.These interior walls 108, 110 could also be made of solid (imperforate)sheet metal, if desired. It will be understood that in this section, thelength of which is indicated as L in FIG. 3, the transversecross-section of the main airflow passageway 82 changes from circular tosquare or rectangular.

[0031] In this transition section, there is preferably located a centralairflow defining member 115 which is rigidly mounted in the ducttransition section 112 and which extends inwardly from the air inlet at46. This airflow defining member has a central longitudinal axisindicated at X which extends through the centre of the air inlet 46. Theexterior of this central airflow defining member is made with strong,perforated sheet metal suitable for high temperature conditions, such asstainless steel. This sheet metal exterior 116 preferably forms atruncated cone as shown in FIG. 3 with the member tapering inwardly inthe direction of the hot air flow. The interior of this air flowdefining member 115 is filled with sound attenuating material which mustbe capable of withstanding the hot temperatures of the air flow rushingpast its sheet metal exterior. In general, the sound attenuatingmaterial must be capable of withstanding airflow temperatures of gasturbine exhaust air, which can be higher than 500° C., and the preferredsound attenuating material is ceramic fiber or mineral wool. In orderthat the perforated sheet metal of the airflow defining member 115 canwithstand these high temperatures for prolonged periods, the sheet metalshould have a thickness of at least 12 gauge. By using this thickergauge, the perforated sheet metal will not bend and distort when itstemperature becomes elevated and subjected to stresses and other forcesacting thereon. This applies to all interior surface materials usedwhere high temperatures may be created. It should also be noted that themetal components in the duct unit that are exposed to the hot air streamshould be constructed so as to allow for quick expansion when exposed tohigh temperature gradients within a few seconds of turbine start up.Also shown in FIG. 3 is a short, connecting flange 118 used to connectthe end 44 of the duct unit to the expansion joint 60 at the outlet ofthe gas turbine. An optional feature of the airflow defining member isthe use of a layer 137 of stainless steel screen arranged behind theperforated sheet metal to prevent the escape of the sound attenuatingmaterial through the holes in the perforated sheet metal.

[0032] Located downstream of the airflow defining member 115 and closeto or next to this member are a series of so-called splitters 120 whichare sound attenuating members and which are rigidly mounted in theairflow passageway system. These splitters divide the main air flowpassageway 82 into smaller passageways 122. Each of these splitters alsohas an exterior formed of perforated sheet metal indicated at 124 andeach splitter is filled with sound attenuating material 126. In thepreferred embodiment illustrated in FIG. 3, there are five evenly spacedsplitters with the central splitter aligned with the central axis X ofthe airflow defining member 115. It will be understood that eachsplitter extends from one interior side wall of the main airflowpassageway 82 to the opposite interior side wall and, although theillustrated splitters extend vertically, it is also quite possible forthe splitters to extend instead in a horizontal direction.

[0033] Preferably, each splitter 120 has a semi-cylindrical nose section128 which can be made of imperforate metal. A tail section 130 of eachsplitter is tapered in the direction of the air flow and this sectioncan be made of perforated metal. In order to provide improved structuralintegrity for each splitter, there can be internal partitions orsupporting members 132, 134. Like the airflow defining member 115, thesplitters should also be constructed so that they are capable ofwithstanding high temperatures of gas turbine exhaust air which can behigher than 500° C. Thus, sound attenuating material filling eachsplitter is preferably heat resistant material such as mineral wool orceramic fiber. The gauge of the sheet metal used to form the exterior ofeach splitter is preferably 12 gauge. Again an optional feature of thesesplitters is the use of a layer of stainless steel screen 133, 135arranged directly behind the perforated sheet metal to prevent theescape of the sound attenuating material. For ease of illustration theuse of the screens 133, 135 is shown in only one of the splitters 120but it will be understood that these layers can be used in all of thesesplitters.

[0034] In accordance with this aspect of the invention, the soundattenuating members or splitters 120 are mounted between the divertervalve or damper 96 and the air inlet 46. Due to the location of thesound attenuating members, they are capable of providing a substantialreduction of the sound levels emitted through either of the air outletsduring use of this sound attenuating duct unit.

[0035] As a result, silencer modules in the by-pass stack section and/orthe main exhaust stack can be simplified by using a larger space betweenadjacent splitters or by even eliminating splitters. This reduces thepressure drop across the sound attenuating members in the exhaustsystem, reduces manufacturing costs, and reduces maintenanceexpenditures.

[0036] The preferred form of the diverter damper 96 is illustratedschematically in FIG. 2. The preferred damper comprises a large, planar,rectangular or square metal flap constructed to withstand the hot airflow temperatures passing by the damper. The preferred metal for thispurpose is stainless steel, for example, type 409 stainless steel. Itwill be understood by those skilled in the art of constructing suchdiverter valves that sheet metal forming the exterior of the damper canbe reinforced or strengthened by suitable supporting frame members thatare covered by the sheet metal. A detailed description of theconstruction of the pivoting damper itself herein is deemed unnecessaryas dampers of this general type are known in this art. For example, adiverter damper of this type is sold by Mannesmann Seiffert under thetrademark ROUTEFLEX. This known diverter damper is pivoted about ahorizontal axis by means of an internal toggle link lever driveconnected to one side of the pivoting damper member.

[0037] The damper 96 pivots about its upper or rear edge on a pivotshaft 140, the ends of which are mounted in the sides of the duct unit.Although the actual mechanism for pivoting the large damper 96 is notshown, it will be appreciated that any suitable known mechanism forpivoting a large damper can be used provided it has sufficient strengthand it does not interfere unduly with the hot air flow through theairflow passageway in either position of the damper. The illustrateddamper 96 is movable between a first position indicated by dash lines at142 in FIG. 2 where the damper directs airflow entering through the airinlet to the first air outlet 80 and a second position shown in solidlines at 144 where the damper directs the air flow to the second airoutlet 64. It will be seen from FIG. 2 that the diverter damper in thefirst position 142 extends substantially horizontally, permitting thehot airflow from the turbine to flow directly and without a significantchange in direction to the outlet 80 where this air flow can pass into aheat recovery unit. In the second position, the damper extends at asubstantial acute angle indicated at 146 to a horizontal plane. Becauseof the slope of the damper or flap and because of the integration ofsloping wall section 94 and the curved interior surface of wall section92, the damper is able to smoothly direct or turn the hot air flow in anupwards direction to permit this air flow to pass smoothly through thesplitter members 68 and eventually through the outlet 64. Thus the slopeof the damper and the slope of the wall sections provides a smootherflow and thus a lower pressure drop than conventional dampers.

[0038] Turning now to a further aspect of the present invention and withinitial reference to FIGS. 1 and 4 of the drawings, the invention alsoprovides an improved heat recovery apparatus that can be used downstreamof the aforementioned air outlet 80. Except for the differences inconstruction noted herein, this heat recovery apparatus can beconstructed in the same manner as the heat recovery steam generator 30illustrated in FIG. 1. This apparatus includes a housing 150 (shown onlyschematically in FIG. 4) having exterior walls, a hot airflow inlet 152and an airflow outlet such as the aforementioned exhaust gas stack 32.The exterior walls of the housing can include horizontal bottom walls154, 156, sloping top walls 158, 160 and horizontal top wall 162.Extending between these bottom and top walls are vertical side walls orside panels 164 and 166. In a known manner, this housing 150 contains anarray of heat exchanging units (shown in FIG. 8) which are rigidlymounted therein. Each heat exchanging unit is adapted for heat exchangebetween the hot air flow that enters through the inlet 152 and a heatexchanging liquid, ie. water, flowing through pipes of the heatexchanging unit. A significant problem with the known heat recoverysteam generators of the past that are constructed in this manner is thatthe hot air flow is simply allowed to flow freely into the large,vertically extending housing containing the heat exchanging units. Theresult is an uneven distribution of the hot air flow as it passesthrough the heat exchanging units. In particular, a major portion of thehot air flow simply flows directly through the lower heat exchangingunits with a substantially lesser amount of hot air flow passing throughthe upper heat exchanging units of the array. This uneven distribution,of course, results in inefficient heat recovery and can further resultin a shortened working life for the heat recovery apparatus because ofpremature failure of pipes and other parts conducting and carrying theheat exchanging fluid, as well as turbulent flow induced fatigue failureof the inner walls of the transition plenum.

[0039] The aforementioned difficulty is substantially alleviated in thepresent invention by the use of aerodynamic diffusers 175, three ofwhich are shown in FIG. 4 and one of which is shown separately in FIG.5. These aerodynamic diffusers are mounted in the region of the airflowinlet 152 and they are preferably mounted one above the other as shown.The number of these diffusers can vary depending upon the size of theheat recovery apparatus and the particular requirements for airflowredirection. As illustrated, these diffusers can be located in arelatively short duct section 177 having a horizontal bottom wall and anupwardly sloping top wall 158. It will be understood that theseaerodynamic diffusers redirect at least a substantial portion of the hotair flow coming from the turbine and entering the housing through theinlet 152 during use of the heat recovery apparatus in order that thehot air flow passes more uniformly through the heat exchanging units.Preferably these aerodynamic diffusers 175 extend horizontally as shownand they extend from one side wall of the duct section to the oppositeside wall. The diffusers 175 and their connections to the side walls areconstructed in a manner known per se so as to allow for quick expansionwhen they are exposed to high temperature gradients within a few secondsof turbine startup. The duct section in which the diffusers are mountedcan be considered a transition duct portion of the housing as itprovides a transition from the lower outlet 80 of the above describedsound attenuating duct unit to the relatively large, verticallyextending housing that contains the heat exchanging units.

[0040] At least a majority of the aerodynamic diffusers 175 are curvedas shown in the drawings from their leading edges 182 (see FIG. 5) tothe rear ends 180 with each diffuser forming a concave curve indicatedat 184 on a top side thereof.

[0041] Turning now to one preferred embodiment of the diffuser 175 asillustrated in FIG. 5, the illustrated diffuser 175 also providesacoustical treatment or sound attenuation in order to reduce the levelof sound passing through the heat recovery apparatus. Thus, in thisembodiment, the curved upper surface of the diffuser is made ofperforated sheet metal stainless steel indicated at 186. It will be seenthat this diffuser has a double wall construction and the bottom surfaceof the diffuser can be made with solid stainless steel sheet metalindicated at 188. Between the two curved walls is suitable soundattenuating material 190 which can fill the interior space of thediffuser. As the hot air passing by these diffusers can still be atelevated temperatures of 500° C. or more, the preferred soundattenuating material is mineral wool because of its low cost and abilityto withstand high temperatures. Other possible sound attenuatingmaterials include ceramic fibers and silica fibers but these materialsare more expensive.

[0042] The leading end of the diffuser can have a semi-cylindrical shapeas shown in FIGS. 5 and 6. Brace plates or connecting plates 192, 194can extend between the two curved walls forming the diffuser and thesehelp to provide the correct spacing between the walls for goodperformance.

[0043] Where sound attenuation by the diffusers is not required, adiffuser of the type illustrated in FIG. 6 can be used. This diffuser200 does not contain any sound attenuating material and both the uppercurved panel 202 and the lower curved panel 204 are made of solidstainless steel sheet metal. Except for these differences, thisaerodynamic diffuser can be the same in its construction and in itsmounting as the diffuser 175.

[0044] With the use of the turning vanes or aerodynamic diffusers ofthis invention, the present heat recovery apparatus has the advantage oflow back pressure in the region of the air flow inlet 152 and thediffusers located a short distance downstream of this inlet. A lowpressure drop is advantageous from an efficiency standpoint and it isachieved by reason of the good aerodynamic design.

[0045]FIG. 7 illustrates the airflow pattern through the heat recoverysteam generator if no aerodynamic diffusers or turning vanes areprovided. Although the hot air flows reasonably smoothly and in onedirection through the transition duct section 177′, the air flow in themuch larger transition section 210 is quite turbulent and virtually isin all directions. This is due to the fact that the hot air flow issimply dumped into the much larger transition space or transitionpassageway formed by the transition section 210. Then, as the hot airflow enters the large box-like housing section 212 wherein heatexchanging units (not shown) are located, the air flows tend to beparallel and horizontal as shown but the amount of air flow passingthrough each level this section varies substantially in practice withmuch more hot air passing through the lower levels indicated at 214 thanthrough the upper levels indicated at 216.

[0046]FIG. 4 illustrates what occurs when aerodynamic diffusersconstructed in accordance with the invention are provided, it will beseen that the air flow through the large transition section 210 is moreevenly distributed over the expanding height of this section and is muchless turbulent. The result is a more uniform distribution of the hot airflow through the section 212 in which the heat exchanging units arelocated.

[0047] In a particularly preferred embodiment, the heat exchanging unitsin the section 212 are in the form of heat recovery steam generatingcoils through which water passes and is heated for steam creation.

[0048] An additional advantage that is achieved through the use of thepresent aerodynamic diffusers and that arises from the more uniform airflow distribution across the heat exchanging units is the elimination orreduction of vibrations in the heat exchanging units or on the insidewalls of the transition section 210, which can otherwise be created. Itwill be appreciated that in the case where there is excessive hot airflow through the lower sections of the heat exchanging units, this airflow, which can be of a fairly high velocity, can create vibrations inthe lower heat exchanging units.

[0049] Also, turbulent airflow can be generated inside the transitionsection 210 if the aerodynamic diffusers are not used. This type ofairflow can produce induced vibration on the inner walls of the section210 and can result in premature fatigue failure of the liner materialand its support structure.

[0050]FIG. 8 illustrates a typical known heat recovery steam generatorin which the series of aerodynamic diffusers (described above) can beused. As illustrated, the steam generator includes a high pressuresuperheater 220 which comprises an array of heat exchanging units in theform of pipes through which water flows. The water, which is a heatexchanging liquid, is heated by the hot gases to generate steam. A ductburner 222 and burner outlet duct 224 can be provided next to thesuperheater 220 on the downstream side. Moving to the right in FIG. 8,the hot gas flow then can pass through a high pressure evaporator 226.Shown on top of the housing and directly above the evaporator 226 is ahigh pressure drum 228 while downstream of the evaporator and extendingthe height of the housing is a high pressure economizer 230 which alsocomprises heat exchanging units.

[0051] Between the economizer 230 and the stack 32 is a low pressuresection of the steam generator. This section can include a low pressuresuperheater 232, a low pressure evaporator 234 and a low pressure drum236 mounted on top of the housing. Mounted above the drum 236 is anintegral deaerator. Arranged between the evaporator 234 and the stack isa feedwater heater 238 that extends the height of the housing as shown.Also illustrated in FIG. 8 is a selective catalytic reducter 240 locatedbetween the high pressure evaporator 226 and the high pressureeconomizer 230. Although one form of heat recovery steam generator hasbeen illustrated in FIG. 8, clearly other forms and other versions ofsuch steam generators are well known in the steam generator art and theuse of the present invention is not limited to the particular steamgenerator that has been illustrated.

[0052] It will be understood by those skilled in the art that variousmodifications and changes can be made to both the sound attenuating ductunit and the heat recovery apparatus as described above withoutdeparting from the spirit and scope of this invention. Accordingly allsuch modifications and changes as fall within the scope of the appendedclaims are intended to be part of this invention.

We claim:
 1. A sound attenuating duct unit suitable for connection to anairflow outlet of a machine having a rotating axial flow member andcomprising: a duct housing having exterior sides and two opposite ends,an air inlet in one of said ends of said housing, and first and secondair outlets with said first air outlet located at the other end of saidhousing, said air inlet being adapted for connection to said airflowoutlet of said machine; interior walls arranged in said housing anddefining a main airflow passageway system which extends from said airinlet to both of said first and second outlets; sound absorbing andthermal insulation material arranged between said interior walls andsaid exterior sides of the duct housing; sound attenuating membersmounted in said airflow passageway system; and a diverter damper mountedin said duct housing and movable between a first position where saiddamper directs air flow entering through said air inlet to said firstair outlet and a second position where said damper directs said air flowto said second air outlet, wherein said sound attenuating members aremounted between said diverter damper and said air inlet so as to reducesound levels emitted through either of said air outlets during use ofsaid duct unit.
 2. A sound attenuating duct unit according to claim 1wherein said sound attenuating members comprise a series of splittersrigidly mounted in said airflow passageway system and dividing said mainairflow passageway system into smaller passageways.
 3. A soundattenuating duct unit according to claim 2 wherein each of saidsplitters has an exterior formed of perforated sheet metal and is filledwith sound attenuating material.
 4. A sound attenuating duct unitaccording to claim 1 wherein said sound attenuating members include acentral airflow defining member rigidly mounted in said housing andextending inwardly from said air inlet, said airflow defining memberhaving a central longitudinal axis which extends through a centre ofsaid air inlet.
 5. A sound attenuating duct unit according to claim 4wherein said central airflow defining member has an exterior formed ofperforated sheet metal and contains sound absorbing material capable ofwithstanding high airflow temperatures of gas turbine exhaust air.
 6. Asound attenuating duct unit according to claim 1 wherein said diverterdamper in said first position extends substantially horizontally and insaid second position extends at a substantial acute angle to ahorizontal plane.
 7. A sound attenuating duct unit according to claim 2including a further series of splitters mounted in said duct housingbetween said diverter damper and said second air outlet and havingexterior surfaces made of perforated sheet metal, each splitter of eachseries containing sound absorbing material.
 8. A sound attenuating ductunit according to claim 2 wherein a layer of stainless steel screen isarranged behind the perforated sheet metal of each of said splitters andacts to prevent escape of the sound attenuating material.
 9. A soundattenuating duct unit suitable for connection to an outlet of astationary gas turbine, said duct unit comprising: a duct housing havingexterior sides, an air inlet in one end of said housing that lies in afirst plane, and first and second air outlets with said first air outletlocated in one of said exterior sides of said housing spaced from saidone end and said second air outlet located in another of said exteriorsides that extends in a second plane arranged at a substantial angle tosaid first plane, said air inlet being adapted for connection to saidoutlet of said gas turbine in order to receive hot air flow from saidgas turbine, interior walls arranged in said housing and definingsidewalls of a main airflow passageway which extends from said air inletto both of said first and second outlets; sound absorbing and thermalinsulation material arranged between said interior walls and saidexterior sides of said duct housing; a series of sound absorbingsplitters rigidly mounted in said airflow passageway and extendingtransversely from one side of said main airflow passageway to anopposite side thereof, said splitters dividing said main airflowpassageway into smaller passageways and containing sound attenuatingmaterial capable of withstanding high temperatures of gas turbineexhaust air; and a diverter damper mounted in said duct housing andmovable between a first position where said damper directs the hot airflow to said first air outlet and a second position where said damperdirects said hot air flow to said second air outlet; wherein said seriesof splitters is mounted between said diverter damper and said air inletso that hot air flow exiting from said smaller air passageway flows to aselected one of said first and second air outlets.
 10. A soundattenuating duct unit according to claim 9 including a central airflowdefining member rigidly mounted in said housing and extending inwardlyfrom said air inlet to said series of splitters.
 11. A sound attenuatingduct unit according to claim 10 wherein said central airflow definingmember has an exterior formed of perforated sheet metal and containssound absorbing material capable of withstanding high temperatures ofgas turbine exhaust air.
 12. A sound attenuating duct unit according toclaim 9 wherein said splitters are made of perforated sheet metal havinga thickness of at least 12 gauge.
 13. A sound attenuating duct unitaccording to claim 9 wherein said diverter damper in said first positionextends substantially horizontally and in said second position extendsat a substantial acute angle to a horizontal plane.
 14. A soundattenuating duct unit according to claim 9 including a second series ofsound absorbing splitters mounted in said duct housing between saiddiverter damper and said second air outlet and having exterior surfacesmade of perforated sheet metal, each splitter of said second seriescontaining sound absorbing material.
 15. A sound attenuating duct unitaccording to claim 9 wherein said air inlet has a circular outerperimeter and said interior walls provide a gradual transition in thetransverse cross-section of said airflow passageway from circular torectangular.
 16. A sound attenuating duct unit according to claim 12wherein a layer of stainless steel screen is arranged behind theperforated sheet metal of each of said splitters and acts to preventescape of said sound attenuating material.
 17. A heat recovery apparatuscomprising: a housing having exterior walls, a hot airflow inlet, and anairflow outlet; an array of heat exchanging units mounted in saidhousing, each heat exchanging unit being adapted for heat exchangebetween a hot air flow and a heat exchanging liquid flowing throughpipes of the heat exchanging unit; and a series of aerodynamic diffusersmounted in said housing in the region of the airflow inlet, wherein saidaerodynamic diffusers redirect at least a substantial portion of hot airflow entering said housing through said airflow inlet during use of saidapparatus in order that said hot air flow passes more uniformly throughsaid heat exchanging units.
 18. A heat recovery apparatus according toclaim 17 wherein said aerodynamic diffusers extend horizontally and arearranged one above another.
 19. A heat recovery apparatus according toclaim 18 wherein said aerodynamic diffusers are rigidly mounted in atransition duct portion of said housing and extend from one interiorwall thereof to an opposite interior wall.
 20. A heat recovery apparatusaccording to claim 17 wherein at least a majority of said aerodynamicdiffusers are each curved from their leading edges to their rear endswith each diffuser forming a concave curve on a top side thereof.
 21. Aheat recover apparatus according to claim 17 in combination with a gasturbine usable for power generation, wherein an outlet of said turbineis connected to said airflow inlet.
 22. A heat recovery apparatusaccording to claim 17 wherein said housing and said array of heatexchanging units together provide a heat recovery steam generatorsystem.
 23. A heat recovery apparatus according to claim 20 wherein eachdiffuser is formed with upper and lower stainless steel sheet metalpanels, each upper panel is made with perforated sheet metal, and eachdiffuser is filled with sound attenuating material.
 24. A heat recoveryapparatus according to claim 20 wherein each diffuser is formed withupper and lower stainless steel sheets which are both imperforate.